An underground coal fire, probably a remnant of a prairie fire during dry conditions last fall, has been growing along Interstate 94, even in frigid North Dakota weather.
State officials are mulling whether to let the below-ground blaze burn out on its own or find money to pay for a backhoe to dig it up and douse it, said Jim Deutsch, who heads the Public Service Commission's mine reclamation division.
Deutsch said the underground fire, about 13 miles west of Bismarck, was discovered a few weeks ago when steam and smoke became noticeable in below-zero temperatures.
The coal bed fire is about 100 yards from the interstate, on the south side. Deutsch said the fire is burning about 4 feet underground, and it's probably about 250 square feet in size.
"It's been growing," Deutsch said. "But there is no threat of it going under the highway."
Darcy Rosendahl, the Transportation Department's director of operations, said the highway officials are monitoring the fire. He said it still is a few feet away from the highway property.
"Of course, if it got in our right of way, we'd have to do something," Rosendahl said.
Such subterranean fires fueled by lignite are not rare in North Dakota, though there have been no reports of them for at least a few years, state geologist Ed Murphy said.
The state has billions of tons of lignite, a relatively soft, brownish low-grade coal. Coal seams can run up to ground level, and once ignited, can burn for decades, Murphy said.
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Explorers Meriwether Lewis and William Clark noted underground coal fires during a visit to North Dakota two centuries ago, Murphy said.
"Coal bed fires are usually related to prairie fires," he said.
An underground coal bed fire in Bowman County, in southwestern North Dakota, smoldered for decades and became somewhat of a tourist attraction until it burned itself out in the late 1970s, Murphy said.
"People used to go there and roast marshmallows," he said.
But Murphy warned against getting close to a coal bed fire. He recalled that about 20 years ago, he was investigating an underground coal fire in North Dakota's Badlands, and fell through the ash and into a red-hot glowing cavern.
"I didn't get burned, but it was pretty warm," Murphy said. "You could have cooked a hot dog in there."
He also noticed the smoldering carcass of a deer that had been trapped in the burning hole.
"These can be dangerous," he said.